The present invention is related to packetized wireless networks, and in particular to a method and apparatus for detecting the start of packet (SOP) in a wireless receiver for operation in a packetized wireless network, wherein the wireless receiver includes a plurality of antennas each having and included in a respective receive chain.
Start of Packet Detection has been an important problem in packetized wireless networks for some time. When designing a wireless packet structure, a preamble (a set of one or more training fields) is usually included. It is preferred that such a preamble be as short as possible to minimize overhead, that is, to devote as much of the packet's bits to data payload. There is therefore a need for methods that can quickly detect the start of a packet that has a short preamble. Note that once the start of packet is detected, there is a need to carry out automatic gain control, timing synchronization, frequency synchronization, and channel estimation before the data payload can be properly processed. This makes it even more important to rapidly detect the start of packet. As a result, in many of today's packetized wireless networks, the maximum range possible with a receiver is often determined more by the ability to rapidly detect the start of packet than the ability to demodulate the encoded data.
What are therefore needed are robust methods for detecting the start of packet transmission.
Start-of-Packet (SOP) detection methods are known, e.g., applicable to wireless local area networks (WLANs) that conform to one of the IEEE 802.11 standards. Commonly assigned U.S. Pat. No. 7,151,759 to Ryan et al., and titled AUTOMATIC GAIN CONTROL AND LOW-POWER START-OF-PACKET DETECTION FOR A WIRELESS LAN RECEIVER describes a SOP detector and a detection method based on RSSI. The contents of U.S. Pat. No. 7,151,759 are incorporated herein by reference.
Commonly assigned U.S. patent application Ser. No. 10/629,383 file Jul. 28, 2003 to Keaney, et al., and titled EARLY DETECTION OF FALSE START-OF-PACKET TRIGGERS IN A WIRELESS NETWORK NODE describes a SOP detector that works together with checking one or more reserved bit locations in a receiver to rapidly ascertain if the SOP provided a false trigger. The contents of patent application Ser. No. 10/629,383 are also incorporated herein by reference.
Above-referenced, related, incorporated herein by reference, and commonly assigned U.S. patent application Ser. No. 10/698,703 filed Oct. 31, 2003 to Hart, et al., and titled INITIAL TIMING ESTIMATION IN AN WIRELESS NETWORK RECEIVER describes a SOP detector that works together with estimating the initial timing.
The SOP detection methods disclosed in each of the above patent applications are applicable to single-input-single-output (SISO) receivers, e.g., receivers arranged for receiving signals that conform to one of the IEEE 802.11 SISO standards, such as IEEE 802.11a, b, and g.
Recently, multiple transceiver receivers such as for operation as multiple-receiver-combining (MRC) wireless nodes and for multiple-input, multiple-output (MIMO) wireless nodes have become more widely available, and there is, for example a draft standard, IEEE 802.11n applicable to wireless local area networks (WLANS) that use MIMO signals. Such MIMO signals have some properties that are different from SISO signals. For example, the present MIMO standard signals include cyclic delay diversity at the beginning of the transmitted packet. This can make detecting the SOP slightly more difficult than in the SISO case.
Thus there is a need for SOP detection methods that work rapidly, and that work well in multi-receiver nodes such as MIMO and MRC nodes.